Which of the following electromagnetic waves has the longest wavelength?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Microwaves
In order of increasing wavelength, the electromagnetic spectrum runs from gamma rays to X-rays, ultraviolet, visible, infrared, microwaves and radio waves.
Option (1) Infrared — Incorrect. Infrared waves (1 mm to 700 nm) lie just beyond the red end of the visible spectrum, on the shorter-wavelength side of the microwaves.
Option (2) Microwaves — Correct. Microwaves are short-wavelength radio waves. Their wavelengths run from about 0.1 m to 1 mm, longer than every other band in the options.
Option (3) Ultraviolet — Incorrect. Ultraviolet (400 nm down to about 1 nm) lies beyond the violet end of the visible spectrum, at much shorter wavelengths.
Option (4) X-rays — Incorrect. X-rays (about 1 nm to \( 10^{-3}\,\mathrm{nm} \)) are among the shortest waves of the spectrum, second only to gamma rays.
NCERT (2026-27):
Summary – “6. The spectrum of electromagnetic waves stretches, in principle, over an infinite range of wavelengths. Different regions are known by different names; γ-rays, X-rays, ultraviolet rays, visible rays, infrared rays, microwaves and radio waves in order of increasing wavelength from 10–2 Å or 10–12 m to 106 m.”